Fatty alcohols have many commercial uses. Worldwide annual sales of fatty alcohols and their derivatives are in excess of US$1 billion. Fatty alcohols are used in diverse industries. For example, they are used in the cosmetic and food industries as emulsifiers, emollients, and thickeners. Due to their amphiphilic nature, fatty alcohols can be formulated or be used per se as nonionic surfactants, which are useful in personal care and household products, for example, in detergents. In addition, fatty alcohols are used in waxes, gums, resins, pharmaceutical salves and lotions, lubricating oil additives, textile antistatic and finishing agents, plasticizers, cosmetics, industrial solvents, and solvents for fats.
One major use for fatty alcohols is in cleaning compositions. On the other hand, fatty alcohols find applicability as surfactants, which are, for example, capable of enhancing oil recovery and/or engine performance. Conventional surfactants comprise molecules having at least one water-solublizing substituent or moiety (e.g., hydrophilic group) and at least one oleophilic substituent or moiety (e.g., hydrophobic group). Examples of hydrophilic groups include, without limitation, carboxylate, sulfate, sulfonate, amine oxide, or polyoxyethylene. Examples of the hydrophobic groups include, without limitation, alkyl, alkenyl, or alkaryl hydrophobes, which typically contain about 10 to about 20 carbon atoms.
Surfactants are typically regarded as the major force behind cleaning products' ability to break up stains, solubilize dirt and soil, and/or prevent their redeposition to surfaces. As such, surfactants are also referred to as wetting agents and foamers, which lower the surface tension of the medium in which they are dissolved. Capable of lowering the interfacial tension between two media or interfaces (e.g., air/water, water/oil, or oil/solid interfaces), surfactants play a key role, and are often the most important component in detergents. Conventional detergent compositions contain mixtures of various surfactants in order to remove different types of soils and stains from surfaces.
The earliest utilized source of hydrophobe groups were natural fats and oils, which were converted into soaps (e.g., carboxylate hydrophile) using base via saponification processes. Coconut and palm oils are to this day used to manufacture soaps and alkylsulfate surfactants. As edible oils became more scarce, it has become increasingly prevalent to manufacture detergents from petrochemicals, using processes such as the Zeigler process to convert petroleum derived ethylene to fatty alcohols. For example, ethylene has been converted into alkyl benzene sulfonate surfactants, which are commonly found in today's detergents and cleaning compositions.
Fatty alcohols can also served as starting materials in the preparation of surfactants and of other cleaning composition ingredients including, for example, alkyl sulfates, fatty ether sulfates, fatty alcohol sulfates, fatty phosphate esters, alkylbenzyl dimethylammonium salts, fatty amine oxides, alkyl polyglucosides, and alkyl glyceryl ether sulfonates. Among these, alkyl sulfates are commonly known due to the ease of their manufacture as well as their improved solubility and surfactant characteristics over traditional soap-based surfactants. However, long-chain alkyl surfactants have less than optimal performance as surfactants or as component(s) of detergents at low temperatures (e.g., about 50° C. or lower, about 30° C. or lower).
While there have been isolated reports that branching, especially towards the middle part of the long-chain alkyl, can reduce solubility of the surfactant, others have described that, in commercial practices, branching in fatty alcohols is highly desirable. See, e.g., R. G. Laughlin, The Aqueous Phase Behavior of Surfactants,” Academic Press, N.Y., (1994), at page 347; but see, Finger et al., Detergent alcohols—the effect of alcohol structure and molecular weight on surfactant properties, J. Amer. Oil Chemicals Society, Vol. 44:525 (1967); Technical Bulletin, Shell Chemical Co., SC:164-80. In addition, K. R. Wormuth, et al., Langmuir, vol 7 (1991):2048-2053, describes the technical advantages observed with a number of branched alkyl sulfates, especially with the “branched Guerbet” type, derived from the highly branched “Exxal” alcohols (Exxon). Phase studies have established a lipophilic ranking (i.e., a hydrophobicity ranking) if highly branched/double tail>methyl branched>linear. Furthermore, patents and applications, including, for example, U.S. Pat. No. 6,008,181 indicates that certain branched or multi-branched fatty alcohol derivatives exhibit improved cleaning capacity, especially at lower temperatures.
Branched fatty alcohols and various precursors are known to have additional preferred properties such as considerably lower melting points, which can in turn confer lower pour points when made into industrial chemicals, as compared to linear alcohols of comparable molecular weights. They are also known to confer substantially lower volatility and vapor pressure, and improved stability against oxidation and rancidity than their linear counterparts. These additional preferred properties, in addition to making branched materials desirable surfactants, make them particularly suited as components or feedstocks for cosmetic and pharmaceutical applications, as components of plasticizers for making synthetic resins, as solvents for solutions for printing ink and specialty inks, or as industrial lubricants.
Those added preferred properties can be alternatively obtained from unsaturated fatty alcohols and precursors. But unsaturation promotes oxidation, leading to short shelf lives and corrosion. Thus desirable properties, e.g., lower melting points, pour points, volatility, and vapor pressure and improved oxidative stability, are better achieved via branching.
Obtaining branched materials from crude petroleum requires a significant financial investment as well as consumes a great deal of energy. It is also an inefficient process because frequently it is necessary to crack the long chain hydrocarbons in crude petroleum to produce smaller monomers, which only then become useful as raw materials for manufacturing complex specialty chemicals. Furthermore, it is commonplace in the petrochemical industry to obtain branched chemicals, such as branched alcohols and aldehydes, by isomerization of straight-chain hydrocarbons. Expensive catalysts are typically required for isomerization, thus increasing manufacturing cost. The catalysts often then become undesirable contaminants that are removed from the finished products, adding yet further cost to the processes.
Obtaining specialty chemicals such as branched alcohols or derivatives from crude petroleum also drains the dwindling resource of petroleum, in addition to the cost and problems associated with exploring, extracting, transporting, and refining. One estimate of world petroleum consumption is 30 billion barrels per year. By some estimates, it is predicted that at current production levels, the world's petroleum reserves could be depleted before 2050.
Finally, processing and manufacturing of surfactants and/or detergents from petroleum inevitably releases greenhouse gases (e.g., in the form of carbon dioxide) and other forms of air pollution (e.g., carbon monoxide, sulfur dioxide, etc.). The accumulation of greenhouse gases in the atmosphere can lead to increase global warming, causing local pollutions and spillage as well as global environmental detriments.
Thus, although it is possible to obtain branched fatty alcohols and derivatives from natural oils and petroleum, it would be desirable to produce these branched materials from other sources, such as directly from biomass.